Fluid under pressure is commonly controlled by means of a valve that includes a valve seat and a mating element that can be controllably positioned relative to the valve seat. However, the position of the mating element relative to the valve seat within the valve is typically controlled from outside the valve with the aid of sliding or rotating seals surrounding some portion of the movable element that protrudes through the valve.
Valves for controlling toxic fluids under pressure are known to obviate sliding or rotating seals by relying upon magnetic fields externally applied to control the operation of internal valve parts. Magnetically-actuated valves of various types are disclosed in the literature (see, for example, U.S. Pat. Nos. 3,783,887; 4,331,171; 4,382,449; 4,114,852; 1,132,570; 3,877,478; 3,774,878; 3,212,751; 4,506,701; 4,350,182; 4,349,042; 4,018,419 cited in the aforementioned related application).